Reported in https://en.wikipedia.org/wiki/Wikipedia:Village_pump_%28technical%29#The_animation_of_thumbnails_gifs (together with other issues):

https://en.wikipedia.org/wiki/File:Non-Native-American-Nations-Territorial-Claims-over-NAFTA-countries-1750-2008.gif has no thumbnail, and trying *any* different thumbnail size only creates a generic "Error generating thumbnail".

The image was uploaded more than three years ago and purging does not help here.

Maybe its 97 frames are too many for the image scaler or whatever:

$:andre\> wget -S -U Malyacko --header 'host: upload.wikimedia.org' 'http://upload-lb.esams.wikimedia.org/wikipedia/commons/thumb/4/40/Non-Native-American-Nations-Territorial-Claims-over-NAFTA-countries-1750-2008.gif/536px-Non-Native-American-Nations-Territorial-Claims-over-NAFTA-countries-1750-2008.gif'
--2013-04-19 15:17:06-- http://upload-lb.esams.wikimedia.org/wikipedia/commons/thumb/4/40/Non-Native-American-Nations-Territorial-Claims-over-NAFTA-countries-1750-2008.gif/536px-Non-Native-American-Nations-Territorial-Claims-over-NAFTA-countries-1750-2008.gif
Resolving upload-lb.esams.wikimedia.org... 91.198.174.234, 2620:0:862:ed1a::b
Connecting to upload-lb.esams.wikimedia.org|91.198.174.234|:80... connected.
HTTP request sent, awaiting response...

HTTP/1.1 500 Internal server error
X-Content-Type-Options: nosniff
X-Powered-By: PHP/5.3.10-1ubuntu3.5+wmf1
Server: Apache
Cache-Control: no-cache
Content-Type: text/html; charset=utf-8
X-Varnish: 2136891041, 798090017, 1861008183
Via: 1.1 varnish, 1.1 varnish, 1.1 varnish
Content-Length: 406
Accept-Ranges: bytes
Date: Fri, 19 Apr 2013 13:17:08 GMT
Age: 0
Connection: keep-alive
X-Cache: cp1031 miss (0), cp3009 miss (0), cp3009 frontend miss (0)
Access-Control-Allow-Origin: *

2013-04-19 15:17:08 ERROR 500: Internal server error.

Version: wmf-deployment
Severity: normal